1. Field of the Invention
The present invention relates generally to optical motion sensors and more specifically to an optical motion sensor for an underwater object.
2. Description of the Prior Art
Detecting the motion of an object as it travels underwater presents difficulties not encountered by instrumentation used in dry environments. These difficulties include protecting the electrical components of the sensing instrumentation from exposure to water and from the extreme changes in pressurization which occur in underwater environments.
The changes in pressurization occur, for example, when an object such as a submarine buoy is launched within the launching barrel of a submarine. As the buoy exits, it exerts tremendous pressure on the sidewalls of the barrels. This pressure can easily damage any instrumentation which is located in the sidewalls of the barrel and which is measuring the exit velocity and acceleration of the buoy.
The instrumentation available among the prior art includes optical motion sensors used in dry environments. For example, U.S. Pat. No. 4,880,966 by Goodrich et al. discloses an optical tachometer sensor for providing an output related to the rotational speed of a rotor shaft of a helicopter. The sensor illuminates a reflective mark on the rotor shaft, with modulated light and focuses this light via a receiving lens arrangement onto a photoelectric sensor. The sensor then provides signals to a conditioning circuitry for controlling output.
U.S. Pat. No. 4,866,269 by Wlodarczyk et al., on the other hand, discloses a fiber-optic detector which senses a light reflective or transmissive pattern of an encoder disk mounted on a cam shaft of an automotive engine. The detector has a sensing head which includes a pair of optical fibers coupled to a light-emitting diode (LED) and a photodiode detector. The LED provides light to the detector head which illuminates a spot on the encoder disk. One of the optical fibers transmits the light to the detector where the received light intensity is translated into an output voltage.
The instrumentation available among the prior art also includes sensors which are non-linear and have a slow response time. As a result, these sensors have low sensitivity and thereby demand accurate positioning at the detecting site. There is thus a need for a sensor which overcomes the above-mentioned problems in the prior art devices.